24 APR 2018
The Hong Kong-Zhuhai-Macau sea crossing links the three cities by the world’s longest bridge over water. Brendon Hooper reports. Engineers have overcome the challenges of complex weather and geological conditions, such as prevailing winds and tidal force, to create a structure built to last 120 years.
When is a bridge not quite a bridge? How about when the bridge, halfway across, turns into an underwater tunnel? Expected to complete in the second quarter of 2018, after an eight-year construction period, the Hong Kong-Zhuhai-Macau bridge (HZMB) is an extraordinary bridge-and-tunnel sea crossing, created to link the three biggest urban centres on China’s Pearl River Delta.
Starting from an artificial island close to Hong Kong airport, the project runs west to another artificial island off Macau. With a total length of just over 55km, the crossing now claims the record as the world’s longest over water – 20 times the length of San Francisco’s Golden Gate Bridge – and includes a 6.7km tunnel, built 40m under the water to allow ships to pass overhead.
With a total length of just over 55km, the crossing now claims the record as the world’s longest over water and includes a 6.7km tunnel, built 40m under the water to allow ships to pass overhead.
The RMB115.9bn ($17.5bn) transport link is a spectacular feat of engineering, which has also necessitated reclaiming vast amounts of land on both sides of the bridge. “For land surveyors, it has been a very demanding project,” says Frankie Yip MRICS, senior land surveyor of the Hong Kong Border Crossing Facility (HKBCF) for Aecom. “First, because it is one of the first large-scale infrastructure projects to adopt building information modelling [BIM] in Hong Kong, and second, due to the unstable condition of the HKBCF artificial island.”
Located to the north-east of Hong Kong International Airport, the facility’s transportation hub provides clearance facilities for goods and passengers using the crossing. The artificial island was reclaimed from around 1.3 km2 of open water, and reinforced by giant steel cylinders, each 23m in diameter and 55m high.
Conventional land reclamation techniques involve the dredging of marine mud from the seafloor, which can cause significant environmental damage. But for the first time in Hong Kong, the border crossing facility’s island was constructed using a non-dredge reclamation technique, whereby steel cylinders were inserted into the mud and filled with inert material, forming a seawall. However, the method caused the island to physically shift, delaying the project. The Highways Department reported that parts of the reclamation shifted by up to six or seven metres.
“It was a huge challenge for our surveying teams,” explains Roy Lim MRICS, resident land surveyor at Aecom. “We needed to constantly update our survey control network to achieve the minimum accuracy limits for subsequent site activities, such as the insertion of the steel bore piles and the construction of the passenger clearance building. After installing monitoring points in various locations to detect land movements, it helped us build a more stable [pile cap] structure.” Although it has been stabilised, the reclaimed land is still settling by 40mm a week, adds Lim.
Yip is confident of the benefits the project will bring. “The bridge has shortened the distance from Hong Kong to Macau and Zhuhai from 160km to just 30km,” he says. The four-hour land journey from Hong Kong to Macau could come down to half an hour, according to official estimates. “With such a time saving, there is no doubt it will benefit the development of Hong Kong’s economy, and increase social communication.”
As the crossing nears completion, behind the fanfare, the project has been at the centre of a controversy over working conditions and safety. Hong Kong’s Labour Department recorded five construction worker fatalities and 234 injuries between 2011 and 2016. However, pro-democracy lawmakers have disputed these figures, arguing there have been at least nine deaths.
With the number of megaprojects of this nature on the rise in markets the world over, the role of construction and infrastructure professionals in upholding good practice and safeguarding worker safety has never been more important. It is therefore imperative that professional organisations such as RICS are at the forefront of efforts to ensure that much-needed infrastructure is not built at the expense of worker safety.